semi-transparent form but opaque Controls in C#

Question

How to make semi transparent form in C# windows form application

I have tried the TransparentKey which makes it full-transparent. and tried Opacit

Answer 1

There is a solution which add semi-transparency to a Control (not Form) :

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        // Apply opacity (0 to 255)
        panel1.BackColor = Color.FromArgb(25, panel1.BackColor);
    }

In visual Studio : (alpha activated only during execution)

Executed on Windows 7 :

Executed on an old WIndows 2003 Server :

Source : https://stackoverflow.com/a/4464161/1529139